150 



Bashford Dean Memorial Volume 



Text-figure 32. 

 The infero'gnathal and postero-infero-gnathal elements of Dinichthys interynedius Nwb., in sections. 



A, functional part; B, blade; C, PIG. /I, floor between blade and cutting part; im, joint impression on PIG. 



as we know, fits in between the two ''picks'' on ASG. It is very massive and of a nearly- 

 quadrangular form in section (Text-figure 32). 



With a more or less deep impression, the tooth is divided from the cutting part (Text- 

 figures 30 and 31, b, c and e). On its front is to be found one or two tooth-like indenta- 

 tions (b and c), which are thin and sharp-edged from both sides. The front of the cutting 

 part is consolidated by a thickening placed on the inside (Text-figure 31 t^). It extends 

 to the top of the second indentation. The edge of the cutting part is long, sharp and 

 finely polished. It works against the edge of PSG. On the hind part of the functional 

 portion, from the posterior corner of the cutting edge down to the jaw blade, is placed a 

 row of small denticles (Text-figures 30 and 31 d). 



The blade is broad and thin on the posterior end, and gets narrower and thicker 

 forward. On the inside (Text-figure 31) under the functional portion, it is thickest and in 

 front fuses with the basal part of the front tooth. The inner surface of the cutting edge is 

 placed deeper than the inner surface of the blade. Thus the upper fore surface of the blade 

 forms a kind of floor in the recess betweenthe blade and the cutting edge (Text-figures 

 31 and 32 /I). 



As a rule the IGis found more or less compressed. Often the whole bone is nearly 

 flat. In reality it was rather strongly curved, especially the anterior or functional portion. 

 The section drawing published by Hussakof (1906, Fig. 2) gives a very good picture of the 

 natural curving of this plate (Text-figure 32). 



Postero-Infero-Gnathal. — This structure (Text-figures 30, 31 and 32 C; Plate 

 VII PIG) is the last plate of the head I have to describe. It has never before been 



